The goal of these studies is to elucidate the mechanisms of induction and prevention of autoimmunity to a peripheral antigen. The elastase gene shows onset of gene expression, which is delayed until after T cells are first exported from the thymus to the periphery. We use the elastase promoter to direct SV 40-T antigen transgene synthesis; the expression of T antigen mimics that of the endogenous elastase gene and therefore permits the study of tolerance and autoimmunity to a protein exhibiting delayed expression. Transgenic mice (ACI-T) expressing SV40-T antigen do not exhibit autoimmunity, despite this delayed expression, although they do show perivascular infiltration in the acinar pancreas. However, simplification of the T cell repertoire by crossing ACI-T mice with mice transgenic for rearranged T cell receptors specific for SV40-T antigen, leads to the early development of autoimmune pancreatitis. As the animals age, tolerance develops, anergic T cells are detectable in the thymus, and depletion of peripheral SV40-Tag reactive T cells occurs in the periphery, coupled with changes in the cytokine profile synthesized by these T cells; cytotoxic T cell activity can, however, be elicited at approximately the same level in double transgenic mice, or in TCR single transgenic mice. We will determine mechanisms that lead to tolerance or autoimmunity in TCR/ACI-T double transgenic mice, and how this process is prevented in single transgenic ACI-T transgenic mice, which express the same antigen but a different T cell repertoire. We will address the following questions: 1. When double transgenic TCR/ACI-T transgenic mice become tolerant, where is this tolerance mediated, in the thymus, in the periphery, or both? 2. Tolerant TCR/ACI-T double transgenic mice exhibit drastic alterations in the nature of CD8 SV40-Tag reactive T cells, with the disappearance of IL-2 producing cells, the reduction of IFN-gamma producing cells, and appearance of IL-4 producing CD8 positive cells; CTL are apparently unaltered. We will determine the relationships between the cells of these different phenotypes to determine if they are the same cells or different cells, with overlapping properties, and we will use ablation techniques, using transgenic mice to determine the lineage relationships between these different CD8 T cell subsets. 3. Why do ACI-T transgenic mice show only mild indications of autoimmunity, while TCR/ACI-T transgenic mice show a dramatic autoimmune phenotype. We hypothesize that this is mediated by immune regulation. We will test this hypothesis and, if true, will characterize the regulatory T cells. 4. A key hypothesis to be tested in this Program Project is that diversification of the autoimmune response is responsible for the maintenance of this chronic disorder. We will test whether diversification of the autoimmune response initiated to SV40-Tag occurs to other acinar antigens. 5. Subsets of T cells producing IL-4 (like TH2 cells), or IFN-gamma (like TH1 cells), inhibit each other. We will test the hypothesis that IL-4 producing CD8 T cells can play a causal role in the prevention and containment of autoimmunity in TCR/ACI-T double transgenic mice. We will elicit large numbers of IL-4 producing cells in vivo, followed by analysis of the capability of these cells in vivo and in vitro.